This edition of "Ask the Author" features a discussion with Andrew Martin, who is a professor of law and chair of the political science department at Washington University in St. Louis. Andrew has done some very influential work on the Supreme Court, including co-authoring a paper on ideological drift of Supreme Court Justices, see here, that will appear in issue four of the Northwestern University Law Review. Andrew is also well-known in political science and empirical circles for his influential Martin-Quinn scores, a technique for measuring the ideology of Supreme Court Justices that he co-developed with Kevin Quinn of Harvard University. For more information on Andrew, please see his personal webpage.

1. What are Martin-Quinn scores? How are they different from other measures of judicial ideology, such as merely looking at the characterization of a Justice's ideology in prominent newspapers such as the New York Times?

Martin-Quinn scores ( are measures that place justices on a common ideological continuum. They do so for each justice in each term since 1937, and are estimated using merits votes derived from the Supreme Court Judicial Database. The scores we produce differ from those derived from newspaper coverage at the time of a justice’s nomination/confirmation in a couple of keys respects. First, the measures are based on actual judicial behavior. Second, the scores are dynamic, allowing the position of each justice to evolve over time. The method employed allows us to make over-time comparisons. Third, the Martin-Quinn scores have been shown to classify votes well across all legal issues, while other measures are typically limited to civil rights and civil liberties cases.

2. How are these scores useful for the non-academic? What do they tell us about the Court?

The scores are useful to anyone who is interested in the politics or decision making patterns of the high court. The scores can be used to understand the politics of the Supreme Court at any point of time, in essence, providing political context to any decision of interest. The scores can also be used to isolate the pivotal (or median) justice in any given term. Many surmise that Justice Kennedy is the pivotal member of the current court; the Martin-Quinn scores provide a scientific basis for that conclusion.

3. Do the Martin-Quinn scores predict judicial behavior? For instance, can they tell us how a particularly Justice might vote in a case? If so, how would your model have predicted the result in certain recent cases?

It depends on what you mean by “predict” (a term often abused in the social sciences). The Martin-Quinn scores themselves cannot be used to predict the outcome in future cases. If we have additional information about the lower court decision, the scores can be used in tandem with that auxiliary information to make predictions. We have not done any prediction since the 2002 term, when we predicted each case in the term before oral argument. In that term, the predictions we generated out-performed those made by panels of legal experts. See for details. Someone could use the Martin-Quinn scores as building blocks for a prediction model, but the scores themselves are not predictive.

4. Let's talk a minute about ideological drift. You are publishing an important paper about ideological drift with Lee Epstein, Kevin Quinn, and Jeffrey Segal in the Northwestern University Law Review. Which of the Justices that you studied showed the most ideological drift over time? Were your findings consistent with what you expected before starting the project?

Almost every justice that we studied from 1937 to the present showed a significant amount of ideological drift. Justices Blackmun, Brennan, and Marshall all drifted significantly to the left during their service on the Court. Surprisingly, so too did Chief Justice Rehnquist, who moved to the left after becoming chief. Justices Black and Frankfurter are the ones who had the biggest move to the right. Going into the project we expected some justices to drift over time, with Justice Blackmun the most salient, given his change of mind in, for example, the death penalty. But the number of justices who exhibited substantial drift was surprising.

5. Of the current Justices, which of them show the most ideological drift? Have any Justices other than Warren Burger drifted one way then drifted back the other way (i.e. from conservative to slightly less conservative to more conservative)?

Of the current justices, Justice Stevens has shown the most ideological drift. In the mid-1980s he turned dramatically to the left, and is now the most liberal member of the Supreme Court. Of the others, we have no data yet on Chief Justice Roberts and Justice Alito. It will be very interesting in ten or twenty years to see where they end up. Justices Thomas and Breyer have been remarkably stable throughout their careers. Justices Kennedy and Ginsburg have moved slightly to the left; Justice Scalia has moved slightly to the right.

As to the second question, Justice Harlan moved to the right and then back to the left during his tenure. So, too, did Justice Douglas.

6. Have you given any thought to the answer to the question of why Justices drift over time? Is there something about the job or life tenure in particular that makes Justices more susceptible to drift?

I’ve thought a little about this, but it is not my speciality. My opinion (which my collaborators may or may not agree with) is that everybody drifts over time. I suspect that if we were to take any political decision maker, whether a Senator, a local school board member, or a Supreme Court justice, and study their behavior for a long period of time we will, in many cases, see some sort of drift. In my mind, only in the cases when the decision maker knew everything and/or was unable to learn would we observe rock-solid stability.

Supreme Court justices are operating in a changing political environment and are asked to make decisions on the most difficult issues of the day. They are constantly bombarded with new information, from their peers, litigants, interest groups, the press, and the clerks with whom they closely work. All of this new information would inevitably cause anybody to alter their beliefs on certain issues. Life tenure likely contributes to the amount of drift we can actually observe; if an elected representative drifts too far, he or she loses her job.

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